Moist to wet surface snow should make loose wet slides remain possible Friday, especially before cooler and cloudier weather arrives late Friday. Also, watch for recently formed soft cornices along ridges.
Summary
Detailed Forecast
Increasing clouds with initially very mild temperatures early Friday should gradually turn to light rain and snow by afternoon with gradually lowering freezing levels. A frontal passage Friday night should cause some new snow, but only light amounts are expected.
Strong melt freeze surface snow should gradually cool with some isolated and shallow wind or storm slabs developing by late Friday at higher elevations.
Recent fresh cornices along ridgelines may still be soft and reactive, likely being weakened by sunshine and warming Thursday. These should remain susceptible to failure Friday. Make sure to give them a wide berth, and be aware of corniced slopes above you.
Less recent snow and ample terrain anchors may limit the avalanche danger below treeline. Many areas at the lowest elevations do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The 15-18 inches of snow that fell about March 14th-15th mainly in the northeast Cascades has settled or melted by a foot and has likely been absorbed into the upper snowpack. The storm last weekend only deposited light amounts of new snow to most of the east slopes.
The DOT crew working at Washington Pass on Monday and Tuesday reports mostly stable overall snow conditions with 4-6 inches of recent snow above the pass and about 2 inches at pass level. One natural loose dry avalanche was seen at about 6500 feet on Silver Star Peak on Tuesday.
Only light amounts of rain and snow fell Wednesday along with a gradual warming trend along the east slopes.
Sunshine and very warm temperatures Thursday has likely created significant surface snowmelt and should lead to a firm melt-freeze crust by Friday.
Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar and lower elevation slopes in the central and southeast Cascades.
Problems
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 27th, 2015 11:00AM
